PhD Defence at DTU Mechanical Engineering

PhD Defence 25th November

Wednesday 28 Oct 15

Contact

Sankhya Mohanty
Researcher
DTU Mechanical Engineering
+4545 25 48 88

Sankhya Mohanty from DTU Mechanical Engineering defends his PhD Wednesday 25th November from 13.00 to 15.00. The defences takes place in Auditorium 54, Building 208, DTU Lyngby.

Abstract
Selective laser melting is an additive manufacturing process allowing the manufacturing of products with complex designs including internal features. However, it is yet to become a standardized industrial manufacturing technique. The process continues to suffer from defects such as distortions, residual stresses, localized deformations and warpage caused primarily due to the localized heating, rapid cooling and high temperature gradients that occur during the process.

While process monitoring and control of selective laser melting is an active area of research, establishing the reliability and robustness of the process still remains a challenge. Experimental studies on selective laser melting have identified several critical factors which affect the process performance. As with most laser-based manufacturing processes, the laser power and the speed of the laser beam feature as important parameters. However, an equally important criterion in case of selective laser melting is the scan pattern i.e. the path which the laser beam follows while processing the layer. Thus, several experimental studies have been devoted towards establishing new useful scan strategies/patterns for selective laser melting.

However, selection of a particular strategy for making a product still remains an issue as most of the scan patterns have Associated problems, such as high temperature gradients, localized overheating, significant deformations, large melt-pools, etc. As the process has been developed to be a precision manufacturing technology, there is a need for effective characterization of the process to establish adequate predictability. However, the usage of focused, high-power lasers as heat sources and the associated multi-physics provides a challenge for modelling large spatial and/or temporal domains.

Simulations of additive manufacturing processes are known to be computationally expensive. The resulting large runtimes prohibit their application in secondary analysis requiring several complete simulations such as optimization studies, sensitivity analysis, etc. In this thesis, a holistic systematic approach to modelling selective laser melting was adopted. Several techniques were investigated for faster yet accurate simulation of the thermal problem for selective laser melting. These faster thermal models were then coupled in appropriate manner for thermometallurgical and thermomechanical simulations of the process.

As a major contribution, a progressive optimization strategy was proposed which allows optimization of real-sized components. A second major contribution was the proposition of a framework for generating reliable, optimized cellular scanning strategy for selective laser melting. Possible improvements to the proposed framework were also identified and were discussed. It is the belief of the author that the field of modelling selective laser melting will improve as a result of the activities carried out during, and presented here in this thesis.